That's a good way to look at it because they are celibate so it's more respectful. Thai monks still sweat, go to the toilet, vomit which would not be ideal to have sacred images nearby or on the body.
Thai monks for hundreds of years have been tattooing sacred mantras, prayers, images and Buddhist protection on lay people's bodies. It is a common practice. Lay people are not celibate and surely the Dharma words on their bodies are very sacred just as well.
I guess the bottom line at our level is whatever we do, there is negative repercussions as well as good points. We have to just see what is more before we do anything.
That's a good point re celibacy. I also like your last comment about everything having good and bad and we just have to weigh up everything and make decisions based on that.
I know that the holy images or mantras cannot be sullied as they are intrinsically holy, but it would be our view of these holy images which could be distorted. For example the well known controversy over the Buddha Bars - whether a Buddha statue should be allowed to be in a bar at all, since the bar is the very antithesis of everything Buddhism represents.
The bar represents samsara's attachments of almost every kind - to relationships, alcohol, food, beauty, sex. However, perhaps the only chance at all of a blessing they could receive would be from a Buddha statue in the bar, though i'm sure that wasn't the motivation behind the Buddha bar. I'm putting myself out on a limb here but i think that it's okay for there to be a Buddha statue in a bar for that reason.